The present application relates to the field of x-ray and computed tomography (CT). It finds particular application with dual-energy CT scanners. It also relates to medical, security, and other applications where obtaining information about the energy spectra of detected radiation would be useful.
CT and other radiographic imaging systems are useful to provide information, or images, of interior aspects of an object. Generally, the object is exposed to radiation, and an image is formed based upon the radiation absorbed by the interior aspects of the object, or rather an amount of radiation that is able to pass through the object. Typically, highly dense aspects of the object absorb more radiation than less dense aspects, and thus an aspect having a higher density, such as a bone or mass, for example, will be apparent when surrounded by less dense aspects, such as fat tissue or muscle. The detectors of a radiographic imaging system are configured to convert the radiographic energy that has traversed the object into signals and/or data that may be processed to produce images.
Multi energy imaging systems may be used to provide additional information about interior aspects of the object, beyond density, such as an atomic number. In particular, a dual energy imaging systems may be used for distinguishing between aspects of the object that have similar densities, such as white and grey brain matter, for example.
Multi energy imaging systems generally involve measuring the absorption characteristics of various aspects of the object for a plurality of energy spectra (e.g., a high energy spectrum and a low energy spectrum). While there are numerous ways to configure a multi energy imaging system for such measurement, one of the more common techniques is known as “source switching.” Source switching is common because it allows for more discrimination between the radiation energy spectra (e.g., relative to techniques that utilize sandwich detectors), which may increase the accuracy of atomic number measurements, for example.
In source switching, the energy spectrum of the radiation is switched between at least two distinguished or different energy spectra. This may be done through a variety of procedures. In one procedure, the voltage applied to the radiation source is varied causing the emitted radiation's energy to vary with the change in voltage. In another procedure, two or more spatially separated sources are configured to alternate radiation emissions (e.g., by alternating power to the sources). Where there are two energy sources, for example, one of the sources may be configured to emit high energy spectrum radiation, while the other may be configured to emit low energy spectrum radiation.
None of the source switching procedures is ideal, however. For example, power to a radiation source cannot be switched on/off or varied instantaneously. Therefore, while the sources are switching the energy spectrum of the radiation, overlap between x-ray emissions may occur. Such overlap is hereafter referred to as source leakage (regardless of whether it results from a change in voltage applied to a single source, or from switching between multiple sources). The non ideal source switching may cause data contamination, by combining different energy spectrum radiation. The data contamination caused by non-ideal switching may result in image artifacts (e.g., bright and dark arcs) that diminish the image quality of the scan.